# Light Falloff(Point Light)

#### Introduction

The light of the point light source is diffused outward in the shape of a sphere. As the diffusion distance increases, the amount of light energy per unit surface area of the sphere becomes smaller and smaller.

How to calculate the light energy?

#### Calculate

In the figure, the unit light energy of a sphere at radius 1 is set to $I_1$, and at radius r is set to $I_2$.

According to `the law of conservation of energy`

, the total energy is constant. So we get the equation

$I_1 4\pi 1^2 = I_24\pi r^2 \\[5px] I_2 = \frac{I_14\pi}{4\pi r^2} \\[5px] I_2 = \frac{I_1}{r^2}$

#### References

All articles in this blog are licensed under CC BY-NC-SA 4.0 unless stating additionally.

Comment